Why did the book held by Rubashov change title between different versions of "Darkness at Noon"?

Question

The English translation of Koestler's Darkness at Noon was made in 1940 by Daphne Hardy. Since the original version of the manuscript was presumed lost, for many years this was the only copy of the book to survive. This changed in 2015 when a carbon copy of Koestler's original German typescript was discovered in Switzerland, and a new translation by Philip Boehm has now been released.

It is interesting to see the differences between the two versions. Hardy was not a professional translator, and had to work in a hurry, so in many cases Boehm's translation reads more "naturally". One particular difference intrigues me though. When Rubashov is meeting the local party leader, Richard, in the museum, he holds a book on his lap so that Richard can identify him (the two had not previously met). In Hardy's version:

On Rubashov’s knee lay a book: Goethe’s Faust in Reclam’s Universal Edition.

While in Boehm's translation:

Rubashov had a book on his lap: the Reclam edition of The Sorrows of Young Werther.

Presumably this change was not introduced by the translators, but was a last-minute amendment by Koestler. Why would he make this change from one of Goethe's works to another? Does the choice of the book have some significance?

Answer 1

A change indicates that Koestler wanted to change the symbolism of the title.

Faust is, of course, a tale of a deal with the Devil, the loss of soul, and all the troubles entailed. This points toward a metaphor being drawn between acting as a Communist and making a deal with the Devil.

Sorrows is about the troubles of a young man, often taken as autobiographical for Goethe himself. This points toward its being symbolic of Koestler's own experiences being reflected in Darkness. Also, Wether dies, which may a foreshadowing of the ending.